A couple weeks ago one of my thesis papers was published in the journal PLOS ONE, titled “Associations of Sedentary Behavior, Sedentary Bouts and Breaks in Sedentary Time with Cardiometabolic Risk in Children with a Family History of Obesity“. It’s a cool study (in my humble opinion), getting a bit of media attention here in Canada, so I’ve been eager to share it here on the blog.
I’m trying something a bit different today by posting a short video blog above for those who would rather watch me explain the study rather than read it (email subscribers can view the video on the blog). Similarly, for those who are more visually inclined, below is a poster based on this study which I presented earlier this year at the Canadian Society for Exercise Physiology conference (hat tip to Zen Faulkes for the excellent poster advice – click to enlarge).
The rationale for this study was simple. Generally, speaking sedentary behaviour (especially screen time) is bad for kids’ health (details here). But in adults, we know that it’s not just total sedentary time that matters, but also patterns in sedentary time.
An example of what I mean can be seen in the above figure, which shows two individuals with the same amount of total sedentary time. However, the person on the left gets most of their sedentary time in prolonged bouts. In other words, when they sit down, they tend to stay sitting for a long time before getting up again. In contrast, the person on the right rarely sits for more than a few minutes at a time without getting up and moving around; they frequently “interrupt” their sedentary time. A wealth of research (both cross-sectional and experimental) suggests that the person on the left (the prolonger) will be at increased health risk compared to the person on right (the breaker)… if they are adults.
In kids, the situation isn’t so clear. Studies by my colleagues Rachel Colley and Val Carson have failed to detect any association between breaks in sedentary time and markers of health in large groups of Canadian and American kids. But those studies looked at kids in the general population. And generally speaking, kids are pretty healthy. As a result, it’s sometimes hard to detect significant associations in kids, because they are just too healthy to begin with. The unique thing about the participants in the present study is that they come from the QUALITY cohort. To be included in this cohort, a child has to have at least one parent with obesity. As I’ve written recently, this means that these kids are also at increased risk of obesity, as well as related health issues. So we thought that it might be worth investigating the relationship between breaks in sedentary time and health in this group of kids, since it might be easier to detect than in the general population.
What did we do?
We measured physical activity and sedentary behaviour patterns in all participants for one week, using an Actical accelerometer. Kids were also asked how much time they spend watching TV, and the amount of time they spend using a computer and playing video games. We measured a range of individual health risk factors (BMI, waist circumference, insulin, glucose, cholesterol, blood pressure, etc). Finally, created a global health risk for each participant, based on their values for each of the individual risk factors.
What did we find?
Irrespective of the total time spent sitting or being physically active, the more frequent the breaks in sedentary time, the lower the global health risk. In other words, frequent breaks from sedentary behaviour seem like a good thing for kids in this cohort. Just to be clear though, this study did not show that increased breaks in sedentary time led to improved health for these kids. We only looked at one time point, so we can’t really say that frequent breaks in sedentary time caused kids to have a better health profile. It’s plausible that being unhealthy led to sitting for more prolonged periods, just like it’s plausible that breaks in sedentary time were good for health. For now we can’t tell which is the chicken, and which is the egg.
Of relevance to this last point, another one of my thesis papers (published in Metabolism, and available for free download here) actually looked at the health impact of making kids sit for prolonged periods, with and without breaks. Interestingly, we found no relationship between breaks in sedentary time and health in a group of healthy children. But that study was looking only at the immediate health-impact of sitting, whereas the current design gets at more of the long-term relationship between breaks and health. But my point is that this study, like any individual study, should not be considered the definitive answer on breaks in sedentary time and pediatric health. This study could be a wonky outlier, or it may be the first of many showing this association in kids with elevated health risk. It’s still interesting and useful, just don’t bet your house that this same relationship will be identical in the next study to come along. This is why replication studies, although boring and unsexy, are incredibly important in terms of actually understanding the behaviours that influence health.
What else did we find?
Our other interesting (but in no way surprising) finding was that screen time was strongly associated with global health risk in both boys and girls. In boys it was video games/computer use that were most strongly associated with health risk, while for girls it was TV viewing. Why the difference? It probably just comes down to the fact that the boys watched a lot more TV than girls in the cohort. Either way, screen time is consistently bad for kids, and this is just one more study to add to the pile.
What is the take-home message?
In this group of kids, frequent breaks from sitting were associated with lower risk factors for chronic disease. We can’t be certain that the breaks caused health to improve, but it’s definitely plausible, especially based on other studies in adults. At the very least, getting kids to break up their sedentary time is unlikely to have any negative health impacts. And if you can get your kids to reduce their screen time, it will almost certainly be beneficial to their health.